Electronically controlled tuning means



Jam 10, 1950 A G, TYNAN ET AL, 2,494,917

ELECTRONICALLY CONTROLLED TUNING MEANS Filed April 22, 1949 Patented Jan. 10, 1950 ELECTRONICALLY CONTRQLLED TUNING MEAN Andrew G. Tynan and James H. Guyton, Kokomo, Ind., assignors to General Motors Corporation,

Detroit, Mich., a corporation of Delaware Application April 22, 1949,l Serial No. 89,132

(Cl. Z50-40) 7 Claims.

This invention relates to means for tuning a radio receiver over a predetermined band of frequencies and more particularly to means for automatically scanning a frequency band and indexing or stopping the tuner on a given station through a control voltage provided by the in-A coming signal. This type of signal control tuner is not new in vgeneral but the previously known types have had certain disadvantages which it is desired to overcome.

one of these has been what might he referred to as coasting .by .or overtraveling, causing stoppng .off station where the incoming signal for control purposes is weak or near the threshold of operativeness and impulses applied to stop thel tuner may be insufficient to cause it to stop immediately or within a predetermined period and it therefore coasts beyond the station or to the far side thereof before it stops, and as a result gives poor reception. In such instances it Would be far better to have the tuner proceed to the next station .rather than stop at all.

.Many of the previous tuners of this type have required an excessive amount of current due to the fact that .the control relay was energized at all times except when the tuning means was in operation which, of course, is a relatively short time.

Lastly, many of these tuners required .an interlocking switch to prevent voperation during the warm-up period.

It is, therefore, an object of our invention to provide a signal .actuated tuner that will proceed to the next station if it coasts through one due to weak control signals.

It is a further `object of our invention `to provide a Signal actuated .tuner that will ,skip a station unless it stops within a predetermined set of limits.

It is a still further object of our invention to provide .a tuner which is economical from a current drain standpoint.

It is a still further object of our invention to provide a signal actuated tuner that does not re,- quire special interlocking means to prevent operation during Warm-up.

With the above and other objects in view, .our invention may be best understood by reference to the following specication and claims .and the illustrations in the accompanying drawing, in which:

.Figure 1 isa circuit diagramof .a control cire.

cuit for a signal actuated tuner embodying our invention; and

'Figure 2 is a circuit diagram of .a control circuit embodying a modied form of our inven tion..

Referring now more specifically to the drawings., it is desired to mention that the control circuits set forth therein are intended to be used with .the conventional radio receiver in which automatic volume control is provided. Various means for volume control have, of course, in the past been used but it is conventional to feed back from the detector a negative voltage which re-V duces the system gain ahead of the detector, and.. therefore, tends to counteract changes therein and assists in maintaining the average output substantially constant. These lines or circuits in receivers are called the AVC lines and it is from this line .that we obtain our control impulse.

Referring now more specically to Figure 1, there is `shown therein a control relay 2 which operates the switching means for the tuning motor for scanning the desired band. Armature 4 actuated by the relay is connected to the main motor .circuit lines 6 and 8, line 6 being directly Y connected to .armature 4, the latter cooperating with a stationary vcontact IG for switch purposes. An insulating member I2 mechanically connects armature 4 with a second .spaced armature I4 which moves therewith, the latter being l.con-- nected directly to resistor It and being able to mechanically engage a fixed contact I8, which is Iconductvely connected to line 26. Resistor I6 is connected to one end of a resistor 22, the opposite end of which is in turn connected to cathodev 24 and grid 26 of the control tube 28, the cathode, of course, likewise being grounded on the opposite side.

A capacitor 30 is connected between resistor I6 and ground and resistor I6 is directly connected through line 32 to screen grid 34 of the tube.

Plate 36 .of the tube is directly connected throughV line 38 to the relay 2, the opposite side of which is .connected to a source of voltage, B+. Line 20 is also connected to B+ as is obvious. Plate 36 is likewise .connected to resistor 40, the opposite ter-l minal of which proceeds to a manually operatedI swtch 42 and thence to ground. Control grid 4.4 of the tube is connected through resistor 46 to the positive terminal of a biasing battery 48, the negative side of which is connected through line 50 to .the AVC line of the receiver previously mentioned. A condenser 52 is connected between control grid 4,4 ,and ground.

When the receiver is turned on and ready to re-A Geil/e Stations, the relay 2 will be energized through the circuit from B+, relay 2, line 38.,-

relay 2, of course, closes the motor circuit through switch 4-I0, and the set is continuously tuned across a given band until a station of predetermined strength is intercepted. At that time a. pulse or relatively large increase in the negative voltage appearing in line 50 occurs to overcome the biasing battery 48 and drives the grid 44 of the tube 28 negative to cause it to cut off, which causes deenergization of the relay 2 and an opening of the motor circuit.

However, in order to overcome the difficulty of stopping ofi station as previously explained, there is provided a delay circuit which consists of the capacitor 30 and the resistance 22 and prevents immediate removal of screen voltage and hence prevents loss of relay control by the tube for a predetermined time, inasmuch as the capacitor 30 discharges through the screen grid 34, circuit of the tube and the resistor 22, and maintains screen voltage for a short time. If, prior to the end of this discharge time, the voltage in the line 50 has disappeared or been substantially reduced, the tube will again be restored to conductive condition and the relay will pick up after being dropped a short time and the station will be skipped and the tuner will proceed to the next strong station, which will avoid any detuning or off station stopping where the signal is not of sufficient strength to cause the tuner to stop with the desired rapidity. When capacitor 30 has been completely discharged and the AVC signal still exists, the plate current of the tube cannot rise to a value sufliciently high to cause the relay to close until such time as the manual switch 42 is closed, which places on the relay and resistance 40 in series` the full B+ voltage and permits the tuner to move on to the next desired station. The determination of the values of capacitor 30 and resistor 22 should be of sufficient value so that the screen voltage remains high long enough to permit station skipping.

` In this embodiment of our invention it will be obvious through the use of a minimum number of parts we have provided a control circuit in which the relay is only energized during tuning cycles, and therefore no interlock is necessary during warm-up period, in which only a single additional tube is used for the control, and also one in which, if the device tends to overtravel or skip due to overtravel on weak signals, it proceeds to, the next station rather than stop oil to one side of the resonance peak, and give poor reception.

Referring now more specically to the modication shown in Figure 2, a control relay 54 is disclosed therein which operates a rstswitch 56 in the main motor lines 58, 50, and at the sameA time simultaneously operates a switch B2 in B+. power supply line 84. Switch 62 is directly con` nected to line 66 which extends from control ref, sistor 68 to one terminal of the control relay 54, the opposite terminal of said relay being con, nected through line 'l0 to plate 12 of control tube., 14. Resistor 68 is connected to cathode 1,6 ofthe tube 14 and likewise to one end of resistor 18, the opposite terminal of which is' grounded. Capacitor 80 is connected between line 66 andground., Control grid 82 of the tube 'I4 is connected through condenser 84 to the plate 86 of a second thermionic tube 88. Plate 86 is in turn connected through line 90 and resistor 92 to B+ supply and grid 82 is connected to resistor 94, the opposite terminal of resistor being grounded. Control grid 98 of' tube 88 is connected to resistor 98 and thence through biasing battery |00 to conductor |02,' which is as in the previous case, line 50, was con-v nected to the AVC control voltage, which must now have a positive polarity with respect to ground. A condenser |04 is connected between the control grid 96 and ground.

Again in this case relay 54 is intended to be energized only at such times as the set is being tuned, and it will be obvious that upon energization of said relay, the motor circuit 58-60 is closed, as is the B+ supply which is connected to line 64. These switches 56 and 62, which operate together, may be manually closed by any suitable mechanical means such as push button |06, which then moves back out of the way so that the switches may open upon deenergization of the coil 54.

Assuming now that the set has been turned on for a suiiicient length of time to enable the tubes y to warm up so that they may properly conduct,

. ance 94. tube 88 and resistance 92 due to thedropv AVC voltage.

the operator forces push button |08 inwardly to close the compound switch 5G-62. This closes the tuning motor circuit 58--50 and the tuning motor operates to cause the set to scan the band. The closure of switch 62 completes a circuit to the relay coil 54 as follows: B+ power supply, line 64, switch 62, line B6, relay coil 54, line 10, tube 14, resistance 18 to ground. Push button |08 moves back out of the way as soon as released and relay coil 54 maintains the switches closed as long as it remains energized. The motor continues the scanning operation until a signal having suiilcient strength for operation is received, and this signal causes a positive voltage to appear in line |02, which is proportional to the nonconducting, since it is biased beyond cut-off by battery |00. Either a positive or a negative pulse may be obtained from the receiver to trigger the circuit and in this case it is assumed that a positive pulse is provided.

This positive pulse overcomes the bias of battery |00 and permits tube 88 to conduct. When the tube conducts, it of course draws plate current and condenser 84 discharges through resistinvoltage on plate 8B. This produces a negative bias on grid 82 and causes this tube 14 to become non-conducting and if the signal for triggering.

is sufliciently strong, the relay 54 will be deene'rglzed and drop its switches 56 and 5'! to stop the set on that station. However, if the signal is weak or if the motor stopping mechanism ooerates too slowly so that the motor stops too late to stop on station and there would be overtravel, there is provided a condenser 80 which is charged by the B+ voltage during the scanning operation and which, for a short time interval after grid 82 has received a negative bias, provides through its discharge current means to maintain the relay 54 in energized condition. If at the end of this period the tube 14 is still non-conducting, the relay will drop and the station will be in tune. If, however` the signal was weak andthe tuner travelled past the station` then the bias on grid 82 would have disappeared and the tube would again be conductive to still maintain the relayV 54 energized and the tuner would pass on to the next station. To `assure positive stopping on sta- (84.l 94. 9.2 and tube 88 inl one case and 80. 88

andliiminthe second case) must be so balanced..v In this form of our invention the relavis only' energized when the set is tuning, Vno interlock is necessary to prevent operation during the To this point tube 88 has been andere.

5, warm-up period, and upon weak signals the 'tuner will pass onl to the vnext Istrong station -rather than ystop 4to Vone side of the resonant tune point.

We claim: l

1. In high frequency signalling apparatus having power actuated tuning means to repetitively scan the frequency band of the apparatus and stop or index due to an incoming sig-nal, means for controlling the power actuated tuner including relay switching means connected to and controlling the power actuated means, a multi-.electrode tube having input and output circuits, the output circuit bein-g connected to the relay, a source of power being connected in series with the relay and the output circuit of the tube so that when the latter conducts the relay will be energized to close the circuit to the power actuated tuning means, a control Velectrode in said input circuit to said tube, conductive means upon which a voltage is developed which is proportional to the strength of the incoming signal connected to the control electrode to control conductive periods of said tube and therefore energizing periods of the relay and electrical storage means connected to the output circuit of the tube to furnish energizing power to the relay for a short predetermined time after tube deenergization by the incoming signal to provide delay after the tube has been biased to cut ofi.

2. In high frequency signalling apparatus having power actuated tuning means to repetitively scan the frequency band of the apparatus and stop or index due to an incoming signal, means for controlling the power actuated tuner including relay switching means connected to and controlling the power actuated means, a multielectrode tube having input and output circuits, the output circuit being connected to the relay, a source of power being connected in series with the relay and the output circuit of the tube so that when the latter conducts the relay will be energized to close the circuit to the power actuated tuning means, a control electrode in said input circuit to said tube, conductive means upon which a voltage is developed which is proportional to the strength of the incoming signal connected to the control electrode to control conductive periods of said tube and therefore energizing periods of the relay, electrical storage means connected to the output circuit of the tube to furnish energizing power to the relay for a short predetermined time after tube deenergization by the incoming signal to provide delay after the tube has been biased to cut off, and manual means to close an energizing circuit to the relay to initiate operation of the tuning means after it has stopped on station due to a received signal.

3. In high frequency signalling apparatus having power actuated tuning means to repetitively scan the frequency band of the apparatus and stop or index due to an incoming signal, means for controlling the power actuated tuner including relay switching means connected to and controlling the power actuated means, a multielectrode tube having input and output circuits, the output circuit being connected to the relay, a source oi power being connected in series with the relay and the output circuit of the tube so that when the latter conducts the relay will be energized to close the circuit to the power actuated tuning means, a control electrode in said input circuit to said tube, conductive means upon which a voltage is developed which is proportional to the strength of the incoming signal connected to the control electro-de to control conductive periods of said tube and therefore energizing periods of the relay, and a resistance and capacity means connected in the output circuit oi the tube and to the electrodes thereof to furnish energizing power after the control grid has been biased to cut off to maintain the relay energized for a predetermined time period to prevent overtravel due to weak. signals.

4. In high frequency signaliing apparatus `having power actuated tuning means `to repetitively scan lthe frequency band or the apparatus and stop or index due to an incoming signal, means for controlling the power actuated tuner including relay switching means connected to and controlling the power actuated means, a multielectrode tube having input and output circuits, the output circuit being connected to the relay, a sourcelo power being connected in series with the relay and the output circuit of the tube so that when the latter conducts the relay will be energized to close the circuit to the power actuated tuning means, a control electrode in said input circuit to said tube, a second electron tube having grid and plate circuits, conductive means upon which a voltage is developed which is proportional to the strength of the incoming signal connected to the grid of the second tube, biasing means in said grid circuit to bias said second tube to cut off unless there is suiiicient voltage on the conductive means to overcome said bias, a capacity resistance coupling circuit between the plate of the second tube and the grid of the rst tube, and capacitor and resistor means in the output circuit of the first tube having a shorter time constant than the capacity resistance coupling between tubes to provide a short energized period after the first tube is biased to cut off to prevent overtravel.

5. In high frequency signalling apparatus having power actuated tuning means to repetitively scan the frequency band of the apparatus and stop or index due to an incoming signal, means for controlling the power actuated tuner including relay switching means connected to and controlling the power actuated means, a multi-electrode tube having input and output circuits, the output circuit being connected to the relay, a source of power being connected in series with the relay and the output circuit of the tube so that when the latter conducts the relay will be energized to close the circuit to the power actuated tuning means, a control electrode in said input circuit to said tube, a second electron tube having grid and plate circuits, conductive means upon which a voltage is developed which is proportional to the strength of the incoming signal connected to the grid of the second tube, biasing means in said grid circuit to bias said second tube to cut off unless there is sufiicient voltage on the conductive means to overcome said bias, a capacity resistance coupling circuit between the plate of the second tube and the grid of the first tube, capacitor and resistor means in the output circuit of the first tube having a shorter time constant than the capacity resistance coupling between tubes to provide a short energized period after the first tube is biased to cut ofi to prevent overtravel and manually operated means in the relay circuit to connect the relay to the power source to cause the power actuated means to proceed on to the next station.

6. In radio receiving apparatus having power actuated means for repetitively scanning the frequency spectrum and a conductor upon which a voltage is developed which is proportional to the strength oi any incoming signal, relay switching means connected to and controlling the power actuated means, a source of power, electron tube means having an input and an output circuit, said relay and source of power connected to the output circuit so that when the tube conducts the relay will close its switch to energize the power actuated means, means for connecting said conductor to said input circuit for the tube, and electrical storage means connected in said output circuit to maintain energization of the relay coil for a certain predetermined time after the tube is biased to cut off by the voltage in the conductor.

7. In radio receiving apparatus having power actuated means for repetitively scanning the frequency spectrum and a conductor upon which a voltage is developed which is proportional to the strength of any incoming signal, relay switching means connected to and controlling the power actuated means, a source of power, electron tube means having an input and an output circuit, said relay and source of power connected to the output circuit so that when the tube conducts the relay will close its switch to energize the power actuated means, means for connecting said conductor to said input circuit for the tube, and capacity and resistance means connected in the output circuit oi' the tube to provide a time delay discharge circuit to delay deenergization of the relay.

ANDREW G. TYNAN.

JAMES H. GUYTON.

No references cited. 

